Method of making a commutator

ABSTRACT

A commutator comprising a commutator sleeve molded of a material having a mechanical and thermal strengths, a plurality of circumferentially arranged spaced commutator segments made out of a conductive ring blank by cutting the outer peripheral surface of said conductive ring blank and secured to the outer peripheral surface of said commutator sleeve, and an insulating material filling the gap between the adjacent ones of said segments, said insulating material being of such character that it can be cut more easily than the conductive ring blank and can be worn off more readily than the same, so that the surface of said insulating material in the commutator is slightly sagged from the surfaces of the adjacent segments after the outer peripheral surface of the conductive ring blank has been cut to separate the segments and is maintained in that state during rotation of the commutator.

I United States Patent 1 1 1111 3,864,821 Ito et a1. 1 Feb. 11, 1975 [54] METHOD OF MAKING A COMMUTATOR 3,468,020 9/1969 Carlson et al 29/597 .482, 07 I2 1969 Y' h' 2 [75] Inventors: Shinichi 1m, Toyokawa; Hide'o Saji, 3 9/597,

' I J both Ndgoyd Primary ExaminerC. W. Lanham [73] Assignee: Nippondenso Co., Ltd., Aichi-ken, Assislan! ExaminerCarl E. Hall Japan Attorney, Agent, or F irm-Cushman, Darby & 22 Filed! Jan. 24, 1973 Cushma [21] Appl. No.: 326,476 [57] ABSTRACT Related Appl'catlon Data A commutator comprising a commutator sleeve Continuation of O- 167273, y 1971, molded ofa material having a mechanical and thermal abandOnedstrengths, a plurality of circumferentially arranged spaced commutator segments made out of a conducl l Forelgn pp Prlorlty Data tive ring blank by cutting the outer peripheral surface Aug. 1, 1970 Japan 45-06743 of said conductive ring blank and secured to the outer 1 peripheral surface of said commutator sleeve, and an [52] US. Cl 29/597, 310/43, 310/235, insulating material filling the gap between the adjacent.

310/236 ones of said segments, said insulating material being of [51] Int. Cl H0lr 43/00 such character that it can be cut more easily than the [58] Field of Search 29/597; 310/233, 235, 236, conductive ring blank and can be worn off more 310/43 readily than the same, so that the surface of said insulating material in the commutator is slightly sagged [56] References Cited from the surfaces of the adjacent segments after the UMTED STATES PATENTS outer peripheral surface of the conductive ring blank 1.845.115 2/1932 Apple 29/597 ux t Cut to the .segments and is min, 3066 387 [M962 Herbst tamed 1n that state durlng rotatlon of the commutator. 3,280,354 10/1966 Unger 3,293,694 12/1966 Taylor. .lr. 29/597 x 3 l2 Draw'ng F'gures c 4 1 METHOD OF MAKING A COMMUTATOR This is a continuation, of application Ser. No. 167,278 filed July 29, 1971, now abandoned.

This invention relates to a commutator which comprises a commutator sleeve molded of a synthetic resin material such, for example, as an asbestos-reinforced phenolic resin material which has a mechanical and thermal strengths, a plurality of commutator segments made out of a conductive ring and secured in spaced relation to the outer peripheral surface of said commutator sleeve, and a soft and brittle insulating material filling the gap between the adjacent ones of said commutator segments and having the surface thereof slightly sagged from the surfaces of said adjacent commutator segments, said insulating material consisting, for example, of a mixture of powdered mica and a small amount of binder or an intersticed resin which can be cut more easily than said conductive ring during cutting of the outer surface of said conductive ring and worn off more readily than said conductive ring when rubbed with a brush during use of the commutator.

Conventional molded commutators have usually been produced by molding a conductive ring of a synthetic resin material having a mechanical and thermal strengths, cutting the outer peripheral surface of said conductive ring to form a plurality of separated segments and forming a groove of predetermined depth between the adjacent ones of said segments by means of a saw. However, the practice of cutting the groove of predetermined depth between the adjacent segments by using the saw, not only adds to the number ofmanhour but also brings about many problems during the production, such as the wear of the saw, overcutting of the grooves and mis-cutting. Furthermore, the chip of the conductive ring or the powder of the brush or segments present, if any, in the grooves, tends to cause an insulation failure. In view of the foregoing, it has been an important subject and a strong desire in the art, to eliminate the step of cutting the grooves.

For eliminating the groove cutting step, i.e. for allowing the insulating material to be left between the segments, it is essential that said insulating material has good electric-shorting preventive and good electric insulating properties, and from this point of view, there has been proposed a commutator having a crystalline mica plate or melamine resin plate with a mineral filler blended therein inserted between the adjacent segments as the insulating material.

This type of commutator, however, has the problems that it generates a large noise, that the brush and the segments are worn off rapidly, and further that the operational characteristics of the associated motor are degraded.

The present inventors conducted various experiments and studies with a view to solving such problems, and found a surprising fact. Namely, the present inventors have found that, while it had been believed that the crystalline mica plate or the melamine resin plate with a filler blended therein is generally easy to work and hence the surface of such insulating material becomes flush with the surfaces of the segments when said segments are made out of a conductive ring by cutting the outer peripheral surface of said conductive ring, the surface of the insulating material actually protrudes about 5 l0 microns above the surfaces of the segments when measured precisely after the cutting, and

such slight projection causes unsatisfactory contact between the brush and the segments, which provides the cause of large noise, and unsatisfactory performance and short service life of the commutator. The formation of such projection is assumably attributed to the facts that both of the insulating materials are high in hardness, that the cutting performance of the cutting tool used is different between the material of the segments and the insulating material, and further that the stress imposed on the insulating material by the cutting tool is alleviated upon passage of said cutting tool over the insulating material, allowing said insulating material to protrude upwardly. At any rate, the present inventors have found that the slight projection of the insulating material has a great influence on the noise problem and the performance of commutator, and this is an epoch-making discovery in the art. The present inventors have also found to their surprise that when a groove is formed between the adjacent segments, it causes a noise to some extent but does not give any influence on the other performances of the commutator, even when the depth of the groove is considerably large.

The object of the present invention is, based on the above knowledge, to provide a very useful commutator which can be produced without the necessity of cutting to a predetermined depth by a saw an insulating material exposed between the adjacent segments on the surface of the commutator and which has aperformance equal to or even better than that of the conventional commutator.

According to the present invention there is provided a commutator which can be produced without involving the step of cutting a groove between the adjacent segments and hence is completely free of the abovedescribed disadvantages of the conventional commutator, and which comprises a commutator sleeve made of a synthetic resin material having a mechanical and thermal strengths, a plurality of commutator segments made out of a conductive ring by cutting the outer peripheral surface of said conducting ring and secured to the outer peripheral surface of said commutator sleeve in spaced relation, and a soft and brittle insulating material filling the gap between the adjacent ones of said commutator segments and having the surface thereof slightly sagged from the surface of said adjacent segments, said insulating material being of such character that it can be cut more easily than said conductive ring during cutting of the outer surface of said conductive ring and can be worn off more readily than said conductive ring during rotation of the commutator in sliding engagement with a brush.

The present invention will be described in detail with reference to an embodiment shown in the accompanying drawing. In the drawing,

FIG. 1 is a perspective view of an embodiment of the commutator according to the present invention;

FIG. 2 is a vertical sectional view of the commutator;

FIG. 3 is a transverse sectional view of the commutator;

FIG. 4 is a fragmentary transverse sectional view showing in an enlarged scale a portion of the commutator;

FIGS. 5 to 7 are a set of views showing sequentially the steps of production procedure of the commutator, of which FIG. 5 is a perspective view of a conductive ring;

FIG. 6 is a perspective view of the conductive ring.

with the segment-separating grooves in the inner surface thereof being filled with a soft brittle insulatin material; and

FIG. 7 is a perspective view of the conductive ring having clinging claws formed on the inner surface thereof; and

FIGS. 8 to 12 are performance characteristic curves of the commutator respectively.

Referring to FIGS. 1 to 4, reference numeral 1 designates commutator segments, 1a clinging claws formed on the inner surface of the respective segments, lb commutator risers and 2 gaps between the adjacent segments. Each gap 2 is filled with a soft brittle insulating material 3 and the surface of said insulating material is slightly sagged from the surfaces of the adjacent segments 1. Reference numeral 4 designates a commutator sleeve made of a synthetic resin material having a mechanical and thermal strengths, such as an asbestos-reinforced phenolic resin.

The commutator of the construction described above is produced in the following manner: First of all, a conductivc ring 6 having a plurality of the segments I joined with each other circumferentially through radially outwardly projecting bridging portions'S and each having a riser lb, as shown in FIG. 5, is made out of a cylindrical conductive blank material (normally a copper pipe) or a planar conductive blank material (normally a copper plate). (the conductive ring 6 may be made out of a cylindrical solid conductive blank material by broaching and in this case, the bridging portions do not project radially outwardly). Then, the soft brittle insulating material 3 is filled in the segment separating slits 2 which are formed in the inner surface of the conductive ring 6 by radially outwardly projecting the bridging portions 5, said insulating material being of such character that it can be cut more easily than the conductive ringduring cutting of the outer peripheral surface of said conductive ring and can be worn off more readily than said conductive ring during rotation of the commutator in sliding contact with a brush. This state is shown in FIG. 6. Thereafter, the clinging claws la are formed on the inner surface of each segment 1 as shown in FIG. 7 and further the commutator sleeve 4 is molded of the synthetic resin material having a mechanical and thermal strengths, within the conductive ring 6. After molding of the commutator sleeve 4, the bridging portions are cut off by cutting the outer peripheral surface of the conductive ring 6, whereby the segments 1 are separated from each other. In this case, the insulating material 3 between the adjacent segments 1 is partially removed from the gaps 2 because of the character described above, and the surface thereof is slightly sagged from the surfaces of the adjacent segments 1, Thus, the commutator shown in FIGS. 1 to 4 is produced.

Examples of the soft brittle insulating material 3 which fills the gap between the adjacent segments 1, include a mixture of a lubricative inorganic or organic powder and a binder. and an intersticed resin.

A powdered mica, powdered talc or boron nitride is suitably used for the inorganic powder, and powdered Teflon is suitably used for the organic powder. The useable binders include natural celluloses and various synthetic resins. When a mixture of the inorganic or organic powder and the binder is used as the insulating 4 material, an organic solvent iseffectively used for facilitating the filling operation.

Asthe intersticed resin, a foamable phenolic resinor foamable epoxy resin is suitably used.

These insulating materials can be filled in the gaps 2 as by spraying or plastering. The use of these foamable resins in the form of'powder in filling the gaps 2 with said resins, is highly advantageous in enhancing the productivity of the commutator.

The depth of the surface of the insulating material sagging from the surfaces of the adjacent segments during cutting of the outer peripheral surface of the conductive ring 6 and rotation of the commutator in sliding contact with the brush can be varied optionally bysuitably selecting the character of the insulating material or the mixing ratio of the ingredients thereof. For instance, when a mixture ofthe inorganic or organic powder and the binder is used as the insulating mate rial, a relatively shallow depression can be maintained between the adjacent segments by increasing the amount of binder used or selectively'using a soft brittle material as the binder. On the contrary, a relatively deep depression can be formed between theadjacent segments 1 by decreasing the amount of binder used or selectively using a hard tough material asthe binder.

Now, the present invention will be further illustrated by way of example.

An insulating material 3 of the following composition was filled in the slits 2 between the adjacent segments 1 of a copper conductive ring 6 of the type shown in FIG. 5.

Composition of the insulating material 3:

50 ISO mica powder parts Nitrocellulose lacquer (binder) 5 'parts Organic solvent 30 parts After the insulating material 3 had been dried, the clinging claws la were formed on the inner surfaces of the respective segments 1 and thereafter, the commutator sleeve 4 was molded of an asbestos-reinforced resin. Finally, the outer peripheral surface of the conductive ring 6 was cut to produce a commutator of the type shown in FIGS. 1 to 3. A 0.05 0.1 mm deep depression was formed in the surface of the commutator between the adjacent segments.

The commutator A of the invention thus produced, a conventional grooved commutator 8 and a grooveless commutator C having a melamine resin as the insulating material between the adjacent segments, were individually mounted in a small-sized, direct-current motor (two brushes, 12 V) and the performances of the respective commutators were compared, with the results shown in FIGS. 8 to 12. In each of these Figures, characters A, B, C represent the commutators A, B, C respectively. FIG. 8 shows the initial performances of the motor with the respective commutatorsmounted therein. It will be seen that the performance of the conventional grooveless commutator C in which the insulating material projects above the surface of the commutator, is inferior to those of the groove-less commutator A of the instant invention and the conventional grooved commutator B. FIG. 9 shows the initial noise levels of the motor with the respective commutators mounted therein and it will be understood therefrom that the noise level of the groove-less commutator of the invention is lowest of all. FIGS. to 12 shows the change in noise level (FIG. 10), the wear of the brush (FIG. 11) and the wear of the segment (FIG. 12) respectively, with the passage of time during a high speed durability test conducted on the motor to determined the performances of the respective commutators. As shown, the groove-less commutator A of the instant invention enables a better result to be obtained than the conventional commutators B, C.

As described above, in the molded commutator of the invention which is produced by using as a blank material, a conductive ring having a plurality of commutator segments joined circumferentially by bridging portions, an insulating material which can be cut more easily than the conductive ring during cutting of the outerperipheral surface of said conductive ring and can be worn off more readily than the conductive ring during rotation of the commutator in sliding contact with the brush, is filled in the gap between the adjacent segments. Owing to the presence of such insulating material, there can be achieved the advantages that the manhour required for the groove-cutting operation required for the conventional commutators can be eliminated, that the troubles which have been encountered in the production of the conventional commutators due to wear of the saw, overcutting of the grooves, miscutting of the grooves and accumulation of the chips in the grooves can be eliminated, and that the degradation of commutator performance due to accumlation of the brush powder in the grooves during rotation of the commutator can be eliminated. Furthermore, since the segments are separated from each other by cutting the outer peripheral surface of the conductive ring, the surface of the insulating material can be sagged slightly from the surfaces of the adjacent segments, and since theinsulating material is worn off always earlier than the segments, by the brush during rotation of the commutator, a good contact can always be maintained between the brush and the segments, and in addition, the noise can be decreased to a level equal to or lower than that of the conventional grooved commutators and the problem of brush wear can be eliminated.

What is claimed is:

1. A process of producing a commutator comprising the steps of: providing an annular conductive ring having a plurality of parallel grooves formed on the inner periphery thereof, said grooves defining commutator segments held together by bridging portions formed across bottoms of said grooves; filling said parallel grooves with a first soft and brittle insulating material which is selected from the group consisting of: an intersticed resin, a mixture of a binder and a lubricative inorganic powder, and a mixture of a binder and a lubricative organic powder; then filling the volume defined by said conductive ring with a second insulating material having greater strength and hardness than said first insulating material; and then cutting the outer peripheral surface of said conductive ring to remove said bridging portions to thereby expose said first insulating material and isolate said commutator segments.

2. A process in accordance with claim 1 wherein the parallel gaps are filled with the first soft and brittle insulating material comprisinga mixture of a binder and a lubricative inorganic powder selected from the group consisting of a powdered mica, powdered talc and boron nitride.

3. A process in accordance with claim 1 wherein the parallel gaps are filled with a first soft and brittle insulating material comprising a mixture of a binder and a powdered Teflon. 

1. A process of producing a commutator comprising the steps of: providing an annular conductive ring having a plurality of parallel grooves formed on the inner periphery thereof, said grooves defining commutator segments held together by bridging portions formed across bottoms of said grooves; filling said parallel grooves with a first soft and brittle insulating material which is selected from the group consisting of: an intersticed resin, a mixture of a binder and a lubricative inorganic powder, and a mixture of a binder and a lubricative organic powder; then filling the volume defined by said conductive ring with a second insulating material having greater strength and hardness than said first insulating material; and then cutting the outer peripheral surface of said conductive ring to remove said bridging portions to thereby expose said first insulating material and isolate said commutator segments.
 2. A process in accordance with claim 1 wherein the parallel gaps are filled with the first soft and brittle insulating material comprising a mixture of a binder and a lubricative inorganic powder selected from the group consisting of a powdered mica, powdered talc and boron nitride.
 3. A process in accordance with claim 1 wherein the parallel gaps are filled with a first soft and brittle insulating material comprising a mixture of a binder and a powdered Teflon. 